Clarke shot a 1-under 72 and Montgomerie had a 74 on the Centenary Course at Gleneagles, where Frenchman Gregory Havret took the first-round lead with a 68.
Nick Dougherty had a 73 to start a late bid to rise from 14th in the standings to the top 10 who qualify automatically. His round contained five birdies and five bogeys on the windy 7,320-yard course with unpredictable greens after recent rain.
Two who could be ousted from the leading 10 on Sunday had mixed fortunes. Ninth-placed Soren Hansen shot a 2-under 71, while Oliver Wilson, 10th, had a 76.
Justin Rose, eighth and at slight risk, shot 73.
Martin Kaymer, 11th, also shot 76. Ross Fisher, 13th, recorded a 72 as the late battle for places on the team heated up.
Ian Poulter, 12th, and Paul Casey, 16th, are playing in Boston this week, both also hoping for wild-card callups from captain Nick Faldo.
Europe defends the Cup from Sept. 19-21 at Valhalla, outside Louisville, Ky.
Clarke, who has five Ryder Cup appearances and is fresh off a victory in last weeks Dutch Open, said he almost convinced himself on Wednesday that he loved this course.
One under was a good score today with the wind and the soft greens, said the Northern Irishman, who is 17th on the list.
Lee Westwood, his old Cup partner, shot 72 and criticized the greens, saying officials should rip them up and redo them all.
Montgomerie, who doubles as the chairman of the tournament, conceded there was a problem.
I think that some greens drain better than these, theres no question, he said. So well have to look into that at a future date.
Montgomerie, who has six wins and two ties in singles matches from his eight Cup appearances, probably needs to win this week to convince Faldo to pick him. He is 20th in the standings after a poor summer.
This was OK. One over is by no means out of this tournament, said the 45-year-old Scot, who expects to be Ryder Cup captain when the event is played here in 2014.
Havret, who won the Scottish Open at Loch Lomond last year, started at the 10th hole and made three birdies before dropping his only shot at No. 1.
Then he birdied Nos. 4-6 and took a two-stroke lead over Christian Cevaer, Paul Broadhurst, Robert Rock and Gary Orr.
Dougherty was a protege of Faldo when he was younger and badly wants to play on his team at Valhalla. Doughertys mother died this year and he has struggled with his form since.
I decided Id do my best to make the team because she always wanted me to play the Ryder Cup, he said. Ive always wanted to play in Nicks team. Im very tired but as long as I give it everything and leave everything out on the course this week, Ill be satisfied.